Just to set the record straight, I just want to say that Carnage is probably my favorite villain in any comic book series. For those who do not know the story origins of Carnage a.k.a. Kletus Kasady, Let me explain it to you.
Kletus Kasady was born and raised into a troubled childhood. He was beaten and physically abused by his father, he tortured and killed the family dog, killed his grandmother by pushing her down a flight of stairs, and tried to kill his own mother by putting a tv in the tub. He was then sent to a home for boys, where his anti-social behavioral patterns made him an easy target for the students and disciplinarians.
He then burnt the home for boys down after killing a disciplinarian and a girl that laughed at him when he asked her out. After being sent to Ryker's Prison for eleven consecutive murders, though Kasady bragged of a dozen more, he shared a cell with Eddie Brock a.k.a venom, a villain that was defeated by Spider-Man. Some time later Brock's symbiote bonded with Brock again and escaped from prison, but Brock left behind a red spawn, since his symbiote was able to reproduce asexually, and bonded with Kasady creating the red monster, known as Carnage.
The character was modeled after the Batman foe, the Joker and he is just as frightening and psychotic as those villains before him. Carnage is such an iconic villain that ought to be showcased because he has the mental stability of the Joker, the powers of Venom, and he is just the coolest villain you will ever see. Carnage has this grandiose essence and presence that is almost infectious, and he almost makes you want to "Paint the whole damn world red".
As it was revealed earlier in the year, Marc Webb said that he wanted to showcase Venom in what would have been "The Amazing Spider-Man 3" and I can only guess that if there was a sequel to that, then Carnage might have made an appearance.
If Carnage does make an appearance, it will probably be after "The Avengers" sequel in 2018. It might be somewhere in the distant Marvel future. If Carnage does appear in the Marvel Cinematic Universe, it would be the coolest thing since "The Avengers" came out.